Abnormalities of the central visual pathways that are produced by well-defined genes or gene combinations will be studied by light and electron microscopical methods. It has been shown that there is a close association between pigment abnormalities of the retinal pigment epithelium and the development of the abnormal pathways, and this relationship will be explored by a detailed survey of the early developmental relationships between the pigment cells, the ganglion cells, and their axons. The details of the abnormal pathways and of the central distribution of the misdirected axons will also be studied in adults by fiber degeneration and autoradiographic methods. In response to the abnormalities of the retino-fugal axons a number of secondary modifications are formed in the geniculo-cortical system. The organization of these secondary modifications will be studied by tracing the pathways in the adults and by studying the developmental sequences producing the abnormality.